I would agree with recommending the Western Digital Caviar 640GB HD or pick up two of them for raid. From my research I did based on the expert advice from others on this forum, the only drive you will find that may be better than that one is the Western Digital Velociraptor which is quite expensive. I was originally wanting the same drive you have picked out but it's not holding up so well in benchmarks etc. The tb technology just hasn't been as refined yet I guess. If you get two 640GB caviars I believe it's cheaper than the 1tb and you end up with more space in the end

For the RAM, if you realy want DDR3 I believe Mushkin has some DDR3 out now too (Mushkin XP PC3-14400 DDR3-1800). You get the expert advice of Mushkin Greg who could give you help with proper timings etc. if you're overclocking. It's a little more expensive though than the OCZ you picked but higher quality and better support I imagine.

I would change your PSU to a Silverstone Strider 750W modular. Having the modular really helps with cleaning up your case for better airflow by getting rid of all the unnecessary cables you won't be using and will make it look with the clear side panel and blue led on your case.

If you're going to overclock you should also check out the new direct contact OCZ Vendetta 2 heatsink and pick up a Noctua PF-12 fan to put on it. You'll lower your temps drastically especially with having the antec 900 case you have. The Noctua fan is silent which is nice because the antec 900 is apparently quite noisy with all the fans going (especially the 200mm beast top mounted).

Looking good though, I'm no exper though so hopefully other people can add to what I've said. Have fun building!